The immediate purpose of this project is to determine the basic features of how a nervous system and its neurons develop in the embryo. The primary features to be investigated include 1) how the characteristic adult morphology of identified neurons arises, 2) how the characteristic adult physiological properties of identified neurons arise, 3) how the connectivity between identified neurons arises, 4) the sequence of major events in laying down the ground plan of the nervous system, and 5) the cell lineages through which identified neurons arise from possibly identifiable neuroblasts. This information will be valuable in itself, but it should also suggest mechanisms of differentiation and should eliminate some hypotheses about differentiation. On the basis of this information, we will expect to make future manipulations of the embryo to directly test developmental hypotheses.